天不会不黑海不会不蓝
[tiān bù huì bù hēi hăi bù huì bù lán]
'The sky never fails to get dark and the sea remains blue always.' It suggests inevitability - some natural facts will remain constant such as day turning into night and seawater always appears blue. In metaphoric terms, it means everyone will meet different challenges and experience the cycle of joys and sorrows, but this world follows its own law.